Almost all homes receive services from public utilities such as water, gas, telephone and electric companies, and most of these services require metering. In the past it was the almost universal practice to install the necessary meters within the building where consumption of the commodity took place, and this required regular access thereto by utility employees to read the meters. Not only was this annoying to the customers, but it also raised complications for the meter readers, who frequently had to return to particular buildings numerous times to find someone at home and thus gain admittance.
To some extent, this problem is alleviated by installing meters external to the building. This expedient is better adapted for use with electricity, because of the nature of the commodity, which does not freeze or pollute the atmosphere, and because of the properties of the metering equipment itself, which is less subject to interference by reason of vagaries of the weather. Accordingly periscopic and other forms of equipment have been devised by which a utility employee outside the house can read a meter within the house, usually in the basement thereof.
A special problem arises when a house is served with gas from a street main. It has been found that the piping sometimes develops a leak, and the leaking gas follows the outer surface of the pipe, sometimes for considerable distances, rather than dissipating into the soil around the pipe near the leak, frequently entering a customer's home through the wall and creating an unpleasant and sometimes hazardous situation.
Technical developments in the optical industry have resulted in the availability of instruments, known for example as Fiberscopes, in which a probe made up of an elongated bundle of fibers of material such as glass is associated with an objective lens at one end and an eyepiece at the other end, to enable vision at the eyepiece of the field of view toward which the objective is directed, even though the bundle may be curved as necessary to avoid obstacles to direct vision between the viewed and viewing sites. Such Fiberscopes are known with two sets of fibers and a built-in light source, so that the field of view may be observed without other illumination.
Apparatus of this sort is quite expensive, and it is not economically practical to install a fiber optics bundle in the home of each customer.
Chemical technology has also advanced to the point where combustible gas indicators known, for example, as Gas-scopes or Explosimeter Indicators are available in which a sample of air is aspirated through a calibrated instrument and the presence of combustible vapors drawn through a probe is made known in quantitative terms. These instruments are also relatively expensive and not adapted for installation generally in every customer's home.